FREQUENTLY ASKED QUESTIONSQuestion 1: What operating systems can I use as a DHCP server? Question 2: What operating systems can I use as a client? Question 3: I did setup the DHCP server but it doesn't work. What am I doing wrong? Question 4: Is it necessary to restart the DHCP server after editing the INI file? Question 5: Is it possible to get the source code of the DHCP server? Question 6: Does the DHCP server support the BOOTP protocol? Question 7: Does the DHCP server support more than one ethernet card? Question 8: Why does IgnoreUnknownClients not work as expected? Question 9: Does the DHCP server support client identifier? Question 10: How to configure the DHCP server for class B networks? Question 11 : I want to establish a pxe boot environment but I don't get it to work. What am I doing wrong? Question 12 : Why is the DHCP Status web page not showing? Question 13 : What is error 10038? And, why does it occur upon termination of the DHCP Server? Question 14 : How can I specify sub-options, e.g. for the vendor specific OPTION_43? Question 15 : How can I add DNS entries and specify a DNS domain? |
| Question 1: What operating systems can I use as a DHCP server? |
Here
is a list of operating systems that have been
used as DHCP Servers so far:
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| Question 2: What operating systems can I use as a client? |
It should work with every operating system (not only windows), since the DHCP server implements a standard protocol. Please tell me about the operating systems that you are using and whether it works or not. Here is a list of clients that it has been used with:
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| Question 3: I did setup the DHCP server but it doesn't work. What am I doing wrong? |
This is probably the question that I hate the most. Here is what I always do to find out what's going on: Setup the IP network by hand. In other words: don't use the DHCP Server, at all. Configure all the necessary things in the network settings of your client machine and don't set "Obtain an IP address from a DHCP server". If you have done this and your network still isn't working there is something very basic wrong, already. There is no hope that the DHCP server is going to help you to solve this problem. Once you have a configuration running, where your two or more computers are setup using manually assigned IP addresses, check your dhcpsrv.ini file once more to make sure that everything that you entered manually appears in the dhcpsrv.ini file. After that, set the "Obtain an IP address from a DHCP server" in the network settings and reboot. If it's not getting an IP address assigned, you need to compare the IP configuration of the manually configured with the automatically configured system. You can use the ipconfig/winipcfg tools. There has to be a difference! If you found that: try to manipulate the dhcpsrv.ini to let the server assign that option that was different in the two configurations. If it still doesn't work then please check your security settings. Especially with Windows Vista it is very likely that you need to open the security settings of your firewall and allow the DHCP server to communicate. Open up ports 67, 68 and 53. If all this didn’t help, then enable the trace (set Trace=1 in the [Settings] section) and send me the dhcpsrv.ini and dhcpsrv.trc files.
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| Question 4: Is it necessary to restart the DHCP server after editing the INI file? |
No. The DHCP server reads the dhcpsrv.ini every time again, when a client requests an IP address. |
| Question 5: Is it possible to get the source code of the DHCP server? |
Maybe. I have absolutely no problem with giving you the source code, as long as I get something back from you. I will not post the source code on the Web, but you can e-mail me and contribute something to make the DHCP server better as it is today. I will consider based on the field of use. Here is a list of examples what kind of information I need to decide:
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| Question 6: Does the DHCP server support the BOOTP protocol? |
Yes. The DHCP server implements the DHCP protocol. And since V1.8 also the BOOTP style requests are supported. |
| Question 7: Does the DHCP server support more than one ethernet card? |
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Yes. It automatically uses all NIC's that it finds and listens for incoming DHCP requests. Windows 2000 (and later OSs) has a little bit of a different behavior than previous Windows operating systems. It doesn't tell you the IP address of an adapter until it is physically connected. The DHCP server since V1.3 supports that as well by implicitly stopping and starting itself whenever a change in the IP configuration occurs. You can also restrict the DHCP Server to certain cards by using the IPBIND_x entries in the [Settings] section or server "virtualization". See the dhcpsrv.ini for details.
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| Question 8: Why does IgnoreUnknownClients not work as expected? |
Sometimes there is confusion about IgnoreUnknownClients. There are two settings that control the behavior of the DHCP server with respect to unknown clients: ConfigureUnknownClients and IgnoreUnknownClients. ConfigureUnknownClients controls whether an unknown client gets an entry automatically generated in the INI file based on IPPOOLs and so on. What makes a client a known client is any kind of client section in the INI file. This can be a client section with wildcards. This client section does not need to contain any IPADDR entry. The IPADDR entry is generated automatically. IgnoreUnknownClients controls how the DHCP server behaves in cases in which no client section is generated by the DHCP server. Sent a NAK to the requesting client or simple ignore the request. Example: [00-40-8C-??-??-??] ; support only clients with mac address starting with 00-40-8C AutoConfig=1 [Settings] ConfigureUnknownClients=0 IgnoreUnknownClients=1 This tells the DHCP server to configure only clients with mac address 00-40-8C-??-??-?? and do not respond to any requests from other kind of clients.
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| Question 9: Does the DHCP server support client-identifier? |
Yes. Set UseClientID=1 and all client sections will be named after the option 61 supplied name of the client. See UseClientID setting for details..
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| Question 10: How to configure IP pools for class B networks? |
The IPPOOL_x setting allows to configure an IP pool like 192.10.1.2-254. This is a class C network with a subnet mask of 255.255.255.0. At first sight it may seem as if the DHCP server would not support class B networks. This would require to define an IP pool like 192.10.2.1-192.10.5.254 with a subnet mask 255.255.0.0. This is indeed possible since V2.3.1. And no special handling is needed anymore. The following describes how to configure the DHCP server to support class B networks in versions prior to V2.3.1: Variant 1: Restrict the DHCP Server to one network interface card (NIC): [Settings] This configuration restricts the DHCP server to one NIC and (very important) sets AssociateBindsToPools=0. This allows to configure a series of IPPOOL_x definitions that in total define all valid IP addresses that the DHCP server shall manage. Of course, this is still restricted to 10 IP pools (approx. 2500 IP addresses in total): IPPOOL_0, ..., IPPOOL_9 Variant 2: Run multiple ("virtual") instances of the DHCP Server: If multiple NICs are to be supported then the variant 1 approach does not work. Because, it is only possible to have one IPPOOL_x per IPBIND_x. In this case the V1.8 feature to run mulitple "virtual" instances comes in handy. dhcpsrv.ini: dhcp1.ini: dhcp2.ini: The two dhcp_.ini files define two seperate instances of the DHCP Server. All the sections and configurations can be specified in the dhcp1.ini or dhcp2.ini as usual. The settings and databases are kept seperately and behave as if two instances of the dhcpsr.exe would have been started with a dedicated ini file for each of them. The only [Settings] that are not "virtualized" are the ones shown in the example above: InstallAsService, ShowBalloonMessages and NotifyTimeout. They can not be "virtualized", because they really define the behavior of the executable process (e.g. installation or icon in the tray). |
| Question 11: I want to establish a pxe boot environment but I don't get it to work. What am I doing wrong? |
The following INI file is the setup for a pxe boot environment for pxelinux. It assumes 192.168.0.2 as the server IP address. [Settings] Trace=1 IgnoreUnknownClients=1 ConfigureUnknownClients=1 AssociateBindsToPools=1 IPBIND_2=192.168.0.2 IPPOOL_2=192.168.0.3-134 [General] LEASETIME=86400 ; lease time of 1 day NEXTSERVER=192.168.0.2 ; tftp server (clients look in option 66 and/or in NEXTSERVER field) OPTION_66=192.168.0.2 ; tftp server BOOTFILE=pxelinux.0 SUBNETMASK=255.255.255.0 DOMAINNAME=mydomain.local DNS_1=192.168.0.2 [TFTP-Settings] ; settings for the integrated tftp server EnableTFTP=1 Root=D:\tftproot\ [DNS-Settings] ; settings for the integrated dns server EnableDNS=1 This configuration works under the assumption that a server side path d:\tftproot\ exists with the needed pxelinux files stored, i.e. pxelinux.0. The integrated DNS is not really needed for a pxe boot environment to work. Please note that the integrated TFTP server (new in V1.9) is configured. If you are already using another TFTP server and want to continue to do so, then please set EnableTFTP=0 and make sure that the external TFTP server is setup accordingly. The same works with Windows 7 and Windows PE boot. If you for example set up a Windows 7 network boot as it is described in the german computer magazin c't 5/2011 page 170ff, then the following INI file will do the job: [SETTINGS] IPPOOL_1=192.168.0.3-254 IPBIND_1=192.168.0.2 AssociateBindsToPools=1 [GENERAL] LEASETIME=86400 NODETYPE=8 SUBNETMASK=255.255.255.0 BOOTFILE=wdsnbp.0 NEXTSERVER=192.168.0.2 [TFTP-SETTINGS] EnableTFTP=1 ROOT=D:\pxe
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| Question 12: Why is the DHCP Status web page not showing? |
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First, please check that the HTTP Server is enabled. [HTTP-Settings] EnableHTTP=1 Root="c:\httproot\" ; the server side pathname to the files served through the http protocol If the HTTP Server is not enabled, then the "Open Status" entry in the context menu is grayed. The status info is provided as a web page and therefore requires the HTTP Server to be enabled. If it still does not work, then make sure that the port number 80 is not already used by another HTTP Server running on your computer. You can move the integrated HTTP Server to another port number with the following setting: [SETTINGS] ... PORT_80=50555 ... Now, the url to access the status web page is http://127.0.0.1:50555. |
| Question 13: What is error 10038? And, why does it occur upon termination of the DHCP Server? |
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In the trace file (dhcptrc.txt) you will see the follwing trace entries: [11/07/2012 07:07:07] DHCP Server is terminating (ignore error messages that follow) [11/07/2012 07:07:07] recvfrom returns with error 10038 This happens every time you terminate the DHCP server. The reason is of technical nature and is by design. There is nothing to worry about, because it is intended behavior. The reason for it lies in the fact that the DHCP Server software uses blocking sockets as a communication resource. The DHCP Server basically is blocked in a socket call and waits for a request from a client. When you terminate the DHCP Server application, then the blocking socket function call is de-blocked by closing the socket. This then leads to the error message 10038. |
| Question 14: How can I specify sub-options, e.g. for the vendor specific OPTION_43? |
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Usually, a DHCP option is either an IP address or subnetmask or a string. You can specify all kind of options and option data using the custom option feature of the DHCP server like this: [General] OPTION_66=192.168.5.1 ; IP address of TFTP server OPTION_60="PXEClient" ; string Some options, especially the vendor specific OPTION_43, are composed of sub-options of different types. It is possible to define OPTION_43 with one sub-option like this: OPTION_43=08 0E "http://load.me" ; This defines OPTION_43 with one sub-option 8. Every sub-option consists of a 1 byte tag (08 in this case), 1 byte length (0E in this case, which is 14 dec) and the data with the given length (http://load.me is a 14 byte string). Unfortunatly the length has to be calculated and entered manually as the second byte in hex format. If there is a second sub-option to be specified, such as an IP address as sub-option 6 then the complete OPTION_43 looks like this: OPTION_43=08 0E "http://load.me" 06 04 192.168.5.1 ; The sub-option 6 also consists of a tag (06), length (04) and data, as you can easily see above. Since V2.4, the error-prone task to manually determine the length of the sub-option is replaced by an auto-len feature. With that the example above reads like this:
OPTION_43=08 ( "http://load.me" ) 06 ( 192.168.5.1 ) ; Everything inside parentheses is automatically prefixed with the length of that data. |
| Question 15: How can I add DNS entries and specify a DNS domain? |
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The integrated DNS function resolves names to IP addresses and vice versa based on the same data repository as the DHCP server itself. All information is stored in the INI file. All clients that have been added to the INI file, automatically or manually, can be resolved. Assuming the following INI file: [General] DOMAINNAME=mydomain.local [00-01-02-03-04-05] IPADDR=10.5.60.7 Hostname=pc1 With this INI file, the DNS function will resolve the IP address 10.5.60.7 to pc1.mydomain.local and vice versa. Say you want to add a DNS record for a client that is not represented in the INI file. A reason why this might be necessary is because you have clients with static IP address on the network not DHCP assigned. Simply add the following lines to the INI file: [IP_10.5.60.8] IPADDR=10.5.60.8 Hostname=pc2 Now the DNS function is able to resolve pc2.mydomain.local. It's IP address is 10.5.60.8. Please note that the section name for pc2 is choosen as IP_... The client section name has no particular function besides being a unique one for each client. Usually this is the MAC address, because this is the identifier used by DHCP. But if the client is only added to the INI file for the purpose of DNS resolution than it is ok to not use the MAC address. |
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